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Date:      Sat, 1 Oct 2011 05:56:26 +0000 (UTC)
From:      Adrian Chadd <adrian@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r225892 - head/sys/mips/mips
Message-ID:  <201110010556.p915uQH6003016@svn.freebsd.org>

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Author: adrian
Date: Sat Oct  1 05:56:25 2011
New Revision: 225892
URL: http://svn.freebsd.org/changeset/base/225892

Log:
  Disable using wait in cpu_idle() until a better solution to timer and
  interrupt handling can be implemented.

Modified:
  head/sys/mips/mips/machdep.c

Modified: head/sys/mips/mips/machdep.c
==============================================================================
--- head/sys/mips/mips/machdep.c	Sat Oct  1 00:31:30 2011	(r225891)
+++ head/sys/mips/mips/machdep.c	Sat Oct  1 05:56:25 2011	(r225892)
@@ -485,9 +485,24 @@ spinlock_exit(void)
 /*
  * call platform specific code to halt (until next interrupt) for the idle loop
  */
+/*
+ * This is disabled because of three issues:
+ *
+ * + By calling critical_enter(), any interrupt which occurs after that but
+ *   before the wait instruction will be handled but not serviced (in the case
+ *   of a netisr) because preemption is not allowed at this point;
+ * + Any fast interrupt handler which schedules an immediate or fast callout
+ *   will not occur until the wait instruction is interrupted, as the clock
+ *   has already been set by cpu_idleclock();
+ * + There is currently no known way to atomically enable interrupts and call
+ *   wait, which is how the i386/amd64 code gets around (1). Thus even if
+ *   interrupts were disabled and reenabled just before the wait call, any
+ *   interrupt that did occur may not interrupt wait.
+ */
 void
 cpu_idle(int busy)
 {
+#if 0
 	KASSERT((mips_rd_status() & MIPS_SR_INT_IE) != 0,
 		("interrupts disabled in idle process."));
 	KASSERT((mips_rd_status() & MIPS_INT_MASK) != 0,
@@ -502,6 +517,7 @@ cpu_idle(int busy)
 		cpu_activeclock();
 		critical_exit();
 	}
+#endif	
 }
 
 int



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